1. Field of the Invention
This invention relates to a recording medium for recording an information, and more particularly to a disc recording medium that is capable of being rotated at a high speed.
2. Description of the Prior Art
Generally, a recording medium for recording an audio information, a video information and a binary information for a computer, etc. has been manufactured in a disc type or a tape cassette type. A disc type of recording medium, hereinafter referred to as "disc recording medium", has been more spotlighted than a tape cassette type of recording medium in that an information is randomly accessed in the high speed. Nowadays, as such a disc recording medium has prevailed a hard disc, an optical disc, a magneto-optical disc and so on. These discs have a very large capacity and high density tracks to record a large amount of information. Also, the disc recording medium has been required to transfer a lot of information at a high speed, that is, to permit high-speed recording and reproduction of an information. The disc recording medium must be rotated at a high speed for a high-speed transfer of information.
A disc is influenced by an exterior interference such as air resistance due to a flow of air occurring upon its rotation. Accordingly, a vibration called a disk flutter is generated at the rotating disc depending on the driving condition of a driver and the state of the disc. In the disc driver, if the disc flutter is larger above the limit value, a head or a pick-up fails to trace signal tracks on the disc accurately to prevent an information from being recorded or reproduced. Because such a disc flutter becomes larger as a disc is rotated at a higher speed, the disc must be rotated below a speed of allowing an access of information. In other words, the disc must be rotated below the limit speed to disappear the disc flutter, the accurate information recording and reproducing can be secured. Accordingly, it is difficult to provide a recording and reproducing speed, that is, a transfer rate of information in the disc above a constant limit speed. Such a limit speed is called as a critical speed and the disc rotates unstably at the critical speed. Due to this, although the disc has a larger capacity and higher density tracks, the rotating speed of the disc is limited at the critical speed.